Formulation of a protein drug can present many challenges for the pharmaceutical scientist. A formulation must be found that stabilizes the protein drug and makes it resistant to degradation by proteolysis, aggregation, misfolding, etc. Especially for engineered proteins that differ in substantial respects to known proteins, finding appropriate stability conditions can be challenging. It is also desirable to have the protein drug be in a format that is convenient for the patient. Desired properties include stability at ambient and refrigerated temperatures; suitability for long term storage, appropriate dosing times and volumes; and minimization of discomfort upon administration.
Etanercept is a dimeric fusion protein consisting of the extracellular ligand-binding portion of the human 75 kilodalton (p75) tumor necrosis factor receptor (TNFR) linked to the Fc portion of human IgG1. The Fc component of etanercept contains the CH2 domain, the CH3 domain and hinge region, but not the CH1 domain of IgG1. When expressed in mammalian cells, it forms a homodimeric complex with two domains of the TNF receptor. Thus, it is an artificial protein that is different from both antibodies and soluble TNF receptors, and therefore subject to different degradation pathways than either. Etanercept is commercially available as ENBREL® (Amgen Inc., Thousand Oaks, Calif.) and is approved to treat moderately to severely active rheumatoid arthritis, moderately to severely active polyarticular juvenile idiopathic arthritis (JIA) in patients ages two and older, chronic moderate to severe plaque psoriasis (PsO) in adults, psoriatic arthritis (PsA) in adults, and active ankylosing spondylitis (AS). Etanercept was first available in a lyophilized formulation to be reconstituted immediately before injection.
Upon reconstitution of the lyophilized product with water for injection, the formulation is 10 mM Tris HCl, 4% mannitol, 1% sucrose, pH 7.4 at about 25 mg/mL. However, this formulation is not stable for storage. It was discovered that a liquid formulation of etanercept could be achieved using arginine to stabilize the protein (see U.S. Pat. No. 7,648,702). An exemplary liquid formulation consists of 50 mg/mL etanercept, 25 mM phosphate buffer, 25 mM L-arginine hydrochloride, 100 mM NaCl, 1% Sucrose at pH 6.3 in water.